IF you replace parts with parts for brakes you need to confirm the system is complete. IF you change parts think drum to disc then you need to update parts. If you modernize systems then terminology changes
You have now in modern drum/disc systems with a engine bay mounted dual reservoir brake master a combination of things
Metering Valve: Holds off pressure to the front disc brakes, allowing the rear drum brakes to engage first for smoother, balanced braking. (NOT TO BE CONFUSED WITH RESIDUAL ) Proportioning Valve: Controls hydraulic pressure to the rear brakes during heavy braking to prevent rear wheel lock-up. Optional Pressure Differential Switch: Detects a loss of pressure in either the front or rear brake lines and triggers the brake warning light on the dashboard.
(hence the combination valve in a 1978 suburban that looks like this). A combination valve is a critical, multi-purpose brass component in vehicle braking systems—typically front disc/rear drum setups—that houses three distinct functions in one unit: a metering valve, a pressure differential switch, and a proportioning valve. It balances brake pressure, prevents rear wheel lock-up during hard braking, and activates a warning light if a system leak is detected.
Now lets talk Residual Valves. (Typically NOT found in combo valves) Because the master is above calipers and drain back will not occur in most modern vehicles.
By adding 2lb (disc side) and 10lb d(rum side) Residual valves to his system. He can go to a frame mounted master.
Now to add more fun. Some dual masters had Residuals built into the master. You could see them in the ports. So if you go by that theory, it would be master - residual - proportion - brakes order. But you will find this all over the place looking online.
This is why what word you use matters and in the automotive industry there is a lot of "overlap" of terms on some items. Brake combo valves being one for sure.
The mechanic masters can update as necessary.
Last edited by hcb3200; 02/16/20266:06 PM. Reason: spelling
